In recent years, in a cellular mobile communication system or the like, as a radio transmission method which can use a large number of channels in the same frequency band so that a large scriber's capacity can be expected, the CDMA (Code Division Multiple Access) system has been widely noticed. On the other hand, an adaptive transceiver device in which interference from another user or an interference caused by a delay wave is removed in transmission by using an adaptive antenna as an antenna for base station and in which no interface is given to another user in transmission has been greatly discussed.
In addition, as an adaptive transceiver device which is appropriate to the CDMA system, a system which controls a directional antenna using such a directivity pattern that an antenna gain is maximum with respect to an arrival direction to perform transmission and reception has been proposed.
FIGS. 7A and 7B (to be referred to as FIG. 7 hereinafter) are block diagrams showing an example of a k-th user adaptive transceiver device in a base station using the conventional DS (Direction Sequence)-CDMA system. FIG. 8 is a block diagram showing an m-th path adaptive reception sub-block 36m of the conventional k-th user adaptive transceiver device shown in FIG. 7. FIG. 9 is a block diagram showing an m-th adaptive transmission sub-block 10m of the conventional k-th user adaptive transceiver device shown in FIG. 7. Here, these drawings show an adaptive transceiver device (CDMA adaptive transceiver device) having a configuration defined as described below. That is, the number of transmission/reception antennas is represented N (N is an integer which is 1 or more), the number of users is represented by K (K is an integer which is 1 or more), and the number of multi-paths and the number of transmission paths per user are represented by M (M is an integer which is 1 or more).
The conventional k-th user adaptive transceiver device is constituted by a second path search circuit 34, a second k-th user adaptive reception unit 35, a first arrival direction estimation circuit 37, reception antenna weight generation circuits 381 to 38M, transmission antenna weight generation circuits 301 to 30M, and a k-th user adaptive transmission unit 9.
N antenna reception signals 1 to N are signals obtained by performing code multiplexing to a desired wave signal and a plurality of interference wave signals received by N antenna elements arranged and closed to each other such that the respective reception signals are correlative to each other. Since the following processes are digitally performed in a base band, it is assumed that the frequencies of the N antenna reception signals 1 to N are converted from a radio band to a base band, and that the N antenna reception signals 1 to N are subjected to analog-to-digital conversion.
The second path search circuit 34 calculates pieces of path delay time information D1 to DM of a desired wave signal of the k-th user from the reception signals multiplexed by a plurality of user signals.
The second k-th user adaptive reception unit 35 is constituted by first delay circuits 31 to 3M, second m-th path adaptive reception sub-blocks 361 to 36M, and a first adder 5.
The first delay circuits 31 to 3M delay the N antenna reception signals 1 to N depending on a multi-path on the basis of the pieces of path delay time information D1 to DM of a desired wave signal which is an output from the second path search circuit 34.
The first adder 5 adds outputs from the second m-th path adaptive reception sub-blocks 361 to 36M to each other to output a k-th user demodulation signal.
The second m-th path adaptive reception sub-blocks 361 to 36M, as shown in FIG. 8, is constituted by despreading circuits 121 to 12M, a reception weighting combining unit 13, and a demodulation unit 16. The second m-th path adaptive reception sub-blocks 361 to 36M receives the antenna reception signals 1 to N and m-th reception antenna weights Wr1 to WrM which are outputs from reception antenna weight generation circuits 381 to 38M.
Despreading circuits 121 to 12N perform a correlative calculation of the antenna reception signals 1 to N and a pseudo random code Ck. It is assumed that the pseudo random code Ck is a complex code consisting of two codes CkI and CkQ which are orthogonal to each other. In this case, each of the despreading circuits 121 to 12N can be realized by one complex multiplier and an averaging circuit operating over a symbol section. Each of the despreading circuits 121 to 12N can also be realized by a transversal filter configuration using the code Ck as a tap weight.
The reception weighting combining unit 13 is constituted by first complex multipliers 141 to 14N and a second adder 15. The outputs from the despreading circuits 121 to 12N are multiplied by m-th reception antenna weights Wm1 to WmN, respectively, and the resultant values are summed up, so that the received signal is generated by an antenna directivity pattern inherent in the m-th path.
A demodulation unit 16 is constituted by a transmission path estimation circuit 17 and a second complex multiplier 18. An output obtained by multiplying an output from the reception weighting combining unit, 13 by a complex conjugate of transmission path estimation outputs serves as an output from the second m-th path adaptive reception sub-block 36m. 
Outputs from the second m-th path adaptive reception sub-block 36m are added to each other by the adder 5, and an output from the adder 5 serves as a demodulated signal from the k-th user.
Next, the first arrival direction estimation circuit 37 receives N antenna reception signals 1 to N as inputs, and estimates the arrival direction of M desired wave signals of the k-th user from reception signals multiplexed by a plurality of user signals. As a method of estimating an arrival direction, e.g., the MUSIC method is known.
The M m-th reception antenna weight generation circuits 381 to 38M calculate m-th reception antenna weights (steering vectors) Wr1 to WrM for forming directivity patterns having gains in a desired signal arrival direction on the basis of M estimated arrival directions θr1 to θrM which are outputs from the first arrival direction estimation circuit 37.
The M m-th transmission antenna weight generation circuits 301 to 30M calculate m-th transmission antenna weights (steering vectors) Wt1 to WtM for forming directivity patterns having gains in a user transmission direction which is the same as the desired signal arrival direction on the basis of the M estimated arrival directions θn1 to θrM which are the outputs from the first arrival direction estimation circuit 37.
When the FDD (Frequency Division Duplex) method is used, a frequency in reception is different from a frequency in transmission. For this reason, a reception antenna weight and a transmission antenna weight must be independently determined on the basis of the estimated arrival direction. When the TDD (Time Division Duplex) method, a frequency in reception is equal to a frequency in transmission. For this reason, a reception antenna weight can also be directly employed as a transmission antenna weight.
The k-th user adaptive transmission unit 9 is constituted by the m-th adaptive transmission sub-blocks 101 to 10M and the third adders 111 to 11N.
The third adders 111 to 11N synthesize outputs from the m-th adaptive transmission sub-blocks 101 to 10M with each other for N transmission antennas, and outputs N synthesized antenna transmission signals 1 to N. The N synthesized antenna reception signals 1 to N are subjected to digital/analog conversion. The frequencies of the N synthesized antenna reception signals 1 to N are converted from a base band to a radio band.
Each of the first adaptive transmission sub-blocks 101 to 10M, as shown in FIG. 9, is constituted by a transmission weighting combining unit 31 and spreading circuits 331 to 33N. The m-th adaptive transmission sub-blocks 101 to 10M receive m-th reception antenna weight Wtm (Wtm1 to WtmM) which are outputs from the M transmission antenna weight generation circuits 301 to 30M and a k-th user transmission signal.
The transmission weighting combining unit 31 is constituted by fourth complex multipliers 321 to 32N. The k-th user transmission signal is multiplied by the m-th transmission antenna weight Wtm (Wtm1 to WtnN) to generate a signal transmitted by an antenna directivity pattern inherent in the m-th path.
The spreading circuits 331 to 33N diffuses N outputs from the transmission weighting combining unit 31 by using the pseudo random code Ck of the k-th user to generate N antenna transmission signals 1 to N. When the pseudo random code Ck is considered as a complex code consisting of two codes CkI and CkQ which are orthogonal to each other, each of the spreading circuits 331 to 33N is realized by one complex multiplier and an averaging circuit operating over a symbol section. Each of the spreading circuits 331 to 33N can also be realized by a transversal filter configuration using the code Ck as a tap weight.
The N antenna reception signals 1 to N include desired wave signal components, interference wave signal components, and thermal noise. In addition, the desired wave signal component and the interference wave signal component include multi-path components. In general, these signal components are arrived from different directions. The conventional CDMA adaptive transceiver device shown in FIGS. 7 to 9 prepares the first arrival direction estimation circuit 37 to estimate the arrival directions of the multi-paths of desired signals, weighting combining of a reception signal in the reception weighting combining unit 13 and weighting combining of a transmission signal in the transmission weighting combining unit 31 are performed such that the signal powers of the paths are maximized. As a result, antenna gains (directivity patterns) of the second m-th path adaptive reception sub-blocks 361 to 36M and the m-th adaptive transmission sub-blocks 101 to 10M are formed to be increased with respect to the arrival directions of the multi-paths of the desired signals in reception.
When the FDD (Frequency Division Duplex) method is used, a frequency in reception is different from a frequency in transmission. For this reason, a reception antenna weight and a transmission antenna weight must be independently determined on the basis of the estimated arrival direction. When the TDD (Time Division Duplex) method, a frequency in reception is equal to a frequency in transmission. For this reason, a reception antenna weight can also be directly employed as a transmission antenna weight.
As a receiver device using an adaptive antenna appropriate to the CDMA system, a device obtained by a spectrum spreading process gain is proposed. Conventionally, the CDMA adaptive receiver device of this type, as described in “Wang, Kohno, and Imai, “Adaptive Array Antenna Combined with Trapped Delay Line Using Processing Gain for Direct-Sequence/Spread-Spectrum Multiple Access System”, Shingakuron Vol. J75-B-II No. 11, pp 815–825, 1992”, “Tanaka, Miki, and Sawahashi, “The Performance of Decision-Directed Coherent Adaptive Diversity in DS-CDMA Reverse Link”, TECHNICAL REPORT OF IEICE. RC596-102, 1996-11”, in reception antenna weight control, a weight control error signal extracted after despreading is used to obtain an SINR improvement effect obtained by a process gain in adaptive control.
FIG. 10 is a block diagram showing another example of the conventional k-th user adaptive receiver device. FIG. 11 is a block diagram showing an m-th path adaptive reception sub-block 40m of the conventional k-th user adaptive transceiver device shown in FIG. 10. Here, these drawings show a k-th user adaptive receiver device (CDMA adaptive transceiver device) having a configuration defined as described below. That is, the number of transmission/reception antennas is represented N (N is an integer which is 1 or more), the number of users is represented by K (K is an integer which is 1 or more), and the number of multi-paths and the number of transmission paths per user are represented by M (M is an integer which is 1 or more).
The conventional k-th user adaptive receiver device is constituted by a second path search circuit 34 and a third k-th user adaptive reception unit 39.
The N antenna reception signals 1 to N are signals obtained by performing code multiplexing to a desired wave signal and a plurality of interference wave signals received by N antennas arranged and closed to each other such that the respective reception signals are correlative to each other. Since the following processes are digitally performed in a base band, it is assumed that the frequencies of the N antenna reception signals 1 to N are converted from a radio band to a base band, and that the N antenna reception signals 1 to N are subjected to analog/digital conversion.
The second path search circuit 34 calculates pieces of path delay time information D1 to DM of a desired wave signal of the k-th user from the reception signals multiplexed by a plurality of user signals.
The third k-th user adaptive reception unit 39 is constituted by first delay circuits 31 to 3M, third m-th path adaptive reception sub-blocks 401 to 40M, a first adder 5, and a decision circuit 6.
The first delay circuits 31 to 3M delay N antenna reception signals 1 to N depending on a multi-path on the basis of pieces of path delay time information D1 to DM of a desired wave signal which is an output from the second path search circuit 34.
The first adder 5 adds outputs from the third m-th path adaptive reception sub-blocks 401 to 40M to each other to output a k-th user demodulation signal.
The decision circuit 6 performs hard decision to an output from the first adder 5 to output a k-th user decision symbol.
Each of the third m-th path adaptive reception sub-blocks 401 to 40M is constituted by despreading circuits 121 to 12M, a reception weighting combining unit 13, a demodulation unit 16, a third complex multiplier 19, an error detection circuit 20, a second delay circuit 21, and a reception antenna weight control circuit 22. The third m-th path adaptive reception sub-blocks 401 to 40M receive antenna reception signals 1 to N and a k-th user decision symbol which is an output from the decision circuit 6.
The despreading circuits 121 to 12N perform correlative calculation between the antenna reception signals 1 to N delayed by the first delay circuits 31 to 3M and the pseudo random code Ck of the k-th user. When the pseudo random code Ck is considered as a complex code consisting of two codes CkI and CkQ which are orthogonal to each other, each of the despreading circuits 121 to 12N is realized by one complex multiplier and an averaging circuit operating over a symbol section. Each of the despreading circuits 121 to 12N can also be realized by a transversal filter configuration using the code Ck as a tap weight.
The reception weighting combining unit 13 is constituted by first complex multipliers 141 to 14N and a second adder 15. The outputs from the despreading circuits 121 to 12N are multiplied by m-th reception antenna weights Wm1 to WmN, respectively, and the resultant values are summed up, so that the received signal is generated by an antenna directivity pattern inherent in the m-th path.
The demodulation unit 16 is constituted by a transmission path estimation circuit 17 and a second complex multiplier 18. An output obtained by multiplying an output from the reception weighting combining unit 13 by a complex conjugate of transmission path estimation outputs serves as an output from the third m-th path adaptive reception sub-block 40m. 
The third complex multiplier 19 multiplies the transmission path estimation output by the k-th user decision symbol.
When the k-th user decision symbol is multiplied by transmission path estimation values of the respective paths, only components related to the phases of the estimation values can be multiplied, and amplitudes calculated by another means may also be multiplied. Another means indicates such a means that a reception power is measured to calculate an amplitude.
The error detection circuit 20 calculates the difference between an output from the third complex multiplier 19 and an output from the reception weighting combining unit 13 to detect a reception antenna weight control error em.
The second delay circuit 21 delays outputs from the despreading circuits 121 to 12N depending on process times of the reception weighting combining unit 13, the demodulation circuit 16, the error detection circuit 20, and the like.
The reception antenna weight control circuit 22 calculates reception antenna weights Wm1 to WmN from a reception antenna weight control error em and an output from the second delay circuit 21.
In a convergence process of adaptive control, a known symbol may also be used in place of the decision symbol.
The N antenna reception signals 1 to N include desired wave signal components, interference wave signal components, and thermal noise. In addition, the desired wave signal component and the interference wave signal component include multi-path components, respectively. In general, these signal components are arrived from different directions. In the conventional CDMA adaptive transceiver device shown in FIGS. 9 and 10, the third m-th path adaptive reception sub-blocks 401 to 40M are independently prepared for the multi-path components of the desired wave signals, and weighting combining of reception signals are performed in the reception weighting combining units 13 such that a ratio of the desired wave signals of the signal components of the respective paths to an interference wave signal power (SIR) is maximized. As a result, the antenna gains (directivity pattern) of the third m-th path adaptive reception sub-blocks 401 to 40M with respect to arrival directions are formed such that the antenna gains are increased with respect to the arrival directions of the signal components of the respective paths and decreased with respect to other delay wave signal components and the interference wave signal component.
As a method of controlling a reception antenna weight which maximizes the ratio of the desired wave signals to an interference wave signal power (SIR), a method of controlling a reception antenna weight on the basis of the MMSE (Minimum Mean Square Error) standards such that the average power of the reception antenna weight control error em is minimized. In the control method based on the MMSE standards, a path arrival direction of a desired wave signal need not be known, and the path arrival direction of the desired wave signal cannot be directly known. Therefore, in order to generate transmission antenna weight for forming a transmission direct ivity pattern as in the conventional CDMA adaptive transceiver device shown in FIGS. 7 to 9, another means for estimating the path arrival direction of the desired wave signal is required.
Here, as adaptive control performed by the MMSE standards, for example, an LMS (Least Mean Square) algorithm is cited.
However, the first disadvantage of the conventional technique is as follows. In the reception unit of the conventional k-th user adaptive transceiver device shown in FIGS. 7 to 9, control for forming a directivity pattern which actively decreases a gain with respect to an interference wave cannot be performed, and performance is poorer than that in the control based on the MMSE standards.
More specifically, in the k-th user adaptive reception unit, reception weighting combining is performed by using an antenna weight appropriate to only the path arrival direction of the estimated desired wave signal.
The second disadvantage is as follows. When the conventional k-th user adaptive receiver device for performing control based on the MMSE standards shorn in FIGS. 10 to 11 is used as an adaptive transceiver device, especially, in the FDD method, a desired wave arrival direction estimation means for calculating a transmission antenna weight must be prepared independently of the reception unit, and the device increases in scale. More specifically, in the k-th user adaptive reception unit using a control method based on the MMSE standards, the path arrival direction of a desired wave signal cannot be directly known.
In the TDD method, the reception antenna weight controlled on the basis of the MMSE standards can be directly used as a transmission antenna weight. In addition, when transmission and reception are controlled on the basis of an arrival direction estimation result, performance in the reception is not poor. On the other hand, when control based on the MMSE standards is performed on the reception side, another arrival direction estimation means for transmission is required, and the structure disadvantageously increases in size.
Therefore, it is an object of the present invention to provide a means for estimating the path arrival direction of a desired wave signal by using a reception antenna weight of a k-th user adaptive reception unit using a control method based on the MMSE standards and generating a transmission antenna weight on the basis of the path arrival direction.